Convert an EXR render from scene-linear colorspace to CIE XYZ
It isn't straightforwards as Cegaton notes.

You could abuse Blender's ridiculous OCIO integration to achieve this however. Save the file as an EXR, and add the following stanza to the OpenColorIO configuration in datafiles/colormanagement:

 - !&lt;ColorSpace&gt;
    name: One-Way XYZ
    family: Input Special
    equalitygroup: ""
    bitdepth: 32f
    description: |
      One way transform to save an XYZ EXR.
    isdata: false
    allocation: uniform
    allocationvars: [0, 1]
    to_reference: !&lt;MatrixTransform&gt; {matrix: 1.0,  0,  0,  0, 0,  1.0,  0,  0, 0,  0,  1.0,  0, 0, 0, 0, 1]}
    from_reference: !&lt;MatrixTransform&gt; {matrix: 0.4124564,  0.3575761,  0.1804375,  0, 0.2126729,  0.7151522,  0.0721750,  0, 0.0193339,  0.1191920,  0.9503041,  0, 0, 0, 0, 1]}


Note that this is a one way transform! Don't use it for anything else. It also assumes the file was saved as default scene referred linear in an EXR.